1). Field of the Invention
The present invention relates generally to a method of processing a semiconductor substrate, and more specifically to a method of forming a layer, such as an oxide layer or a nitrogen containing layer, on a semiconductor substrate.
2). Discussion of Related Art
Semiconductor processing often comprises the heating of a substance within the chamber so that the substance combusts or otherwise decomposes to form a gas. A substrate, located in the chamber, is then exposed to the gas so that a layer is grown on the substrate. A problem with such a process is that the combustion or decomposition temperature is often too high for purposes of forming the layer. A temperature of formation which is too high results in the layer formation too fast for purposes of proper control.
For example, the manufacture of a metal oxide semiconductor (MOS) transistor involves the step of forming a gate oxide layer by exposure of a semiconductor substrate to oxygen, usually in the form of water vapor. During the formation of the gate oxide layer it is advantageous also to expose the substrate to a chlorine containing gas, resulting in chlorine being taken up in the gate oxide layer. Chlorine has various uses--see for example Silicon Processing for the VLSI Era by S. Wolf et al, page 215. The chlorine is obtained from a gas such as dichloroethylene (DCE) which is combusted with oxygen to form HCl gas. The minimum combustion temperature of DCE is about 700.degree. C., below which DCE does not fully combust, resulting in carbon in the combusted gas which is taken up by the gate oxide layer. At a temperature of 700.degree. C. and above, however, the growth rate of the gate oxide layer is too fast, resulting in less control over the formation thereof. This is troublesome, especially for purposes of forming a stable, uniform gate oxide layer of less than 20 .ANG. thick.
Another example of the formation of a layer by the decomposition of a substance at an elevated temperature can be found in the specification of U.S. patent application Ser. No. 08/775,571 wherein N.sub.2 O gas is decomposed at a temperature of between 900.degree. C. and 1050.degree. C. to form a gas. The gas is then used for purposes of growing an oxy-nitride layer.